1. Technical Field
The present invention relates to a liquid ejection head such as an ink jet recording head and a liquid ejection apparatus having the same, and more specifically to a liquid ejection head that ejects liquid containing tabular particles such as metal pigment and a liquid ejection apparatus having the same.
2. Related Art
A liquid ejection apparatus has a liquid ejection head that is capable of ejecting liquid as liquid droplets from nozzles and is configured to eject a variety of liquid from the liquid ejection head. Typical example of liquid ejection apparatus includes an image recording apparatus such as an ink jet recording apparatus (printer) that has an ink jet recording head (hereinafter, referred to as “recording head”) and is configured to perform recording by ejecting ink in the form of liquid as ink droplets from the nozzles of the recording head. Further, the liquid ejection apparatus is also used to eject a variety of liquid such as a color material used for color filters of liquid crystal displays, an organic material used for organic electro luminescence (EL) displays, and an electrode material used for making electrodes. The recording head for image recording apparatus ejects ink in the form of liquid, and a color material ejection head for display manufacturing apparatuses ejects solution of color materials, red (R), green (G) and blue (B). Further, an electrode material ejection head for electrode manufacturing apparatuses ejects an electrode material in the form of liquid, and a bio-organic material ejection head for chip manufacturing apparatuses ejects a bio-organic solution.
The liquid ejection head using an ink jet technique includes a plurality of nozzles, pressure chambers which are provided for each of the respective nozzles, a common liquid chamber (also referred to as reservoir or manifold) which are provided for a plurality of pressure chambers, and liquid flow paths such as a supply path that connects the common liquid chamber and each of the pressure chambers. The liquid ejection head is configured to eject liquid from the nozzles when a pressure change is applied to liquid in the pressure chambers by driving a pressure generating unit such as a piezoelectric element and a heat generating element.
Recently, as described in JP-A-2012-001581, ink jet technology is applied to ejection of metallic ink containing metal particles as pigment. In order to achieve metallic gloss on the printed material which is printed by using metallic ink, the metal particles should have a surface as flat as possible. Accordingly, the metal pigment contained in the metallic ink is made from tabular (flake like) particles.
FIG. 8 is a schematic view showing an example of configuration of a liquid flow path of the recording head. In FIG. 8, the arrow indicates a flow of ink. As shown in the figure, the respective pressure chambers 51 communicate with a reservoir 53 (common liquid chamber) via ink supply paths 52. The ink supply paths 52 have a cross-sectional area which is sufficiently smaller than that of the pressure chambers 51. As a result, the cross-sectional area of the flow paths significantly changes at the boundary between the ink supply paths 52 and the pressure chambers 51. As ink flows from the reservoir to the pressure chambers 51 via the ink supply paths 52, the cross-sectional area of the flow paths increases, which causes the flow speed of ink flowing from the ink supply paths 52 to the pressure chambers 51 to decrease. In particular, the flow speed in an area (which is denoted by X in FIG. 8) outside the extension area of the ink supply paths 52 into the pressure chambers 51 is lower than in the extension area. This causes a boundary layer separation at the boundary between the area X and the extension area, and thus generates turbulent flow, that is, eddying flow in the pressure chambers 51. The eddying flow causes the local flow of the tabular particles in metallic ink moving in circle (revolve). The revolving flow of the tabular particles in a small area in the pressure chambers causes an adverse effect to ink ejection. Specifically, problems such as turning of flying direction of ink ejected from the nozzles 54 and ejection failure of ink from the nozzles 54 may occur.
Such problems are not limited to occur in the ink jet recording heads that eject metallic ink, but also occur in other liquid ejection heads that eject liquid containing tabular particles.